Method and apparatus for measuring pipe coating thickness

ABSTRACT

This invention relates to a method and apparatus for monitoring the amount of coating material that has been applied to a pipe. Opposed parallel sensing arms are positioned in contact with the coated pipe. One of the arms is movable relative to the other arm and in response to variations in the thickness of the coating. A direct mechanical linkage may be utilized to provide a readout of the variations in coating thickness or the movements of the arm may be used to vary the output of a potentiometer to provide an electrical readout. The potentiometer output may, in turn, be coupled with digital circuitry to provide a digital display. The circuitry may also include logic circuitry which will translate the variations in readings into positive or negative deviations from a desired predetermined coating thickness. The invention also contemplates coupling the output from the monitoring device with the controls for the coating plant so as to automatically compensate for excesses or deficiencies in the coating thickness.

This invention relates to a method and apparatus for monitoring theamount of coating material applied to a section of pipe.

All pipe which is placed underground or under water is coated with acorrosion protection coating. Whenever pipe is to be laid under water,it is also frequently necessary to apply a weight coating to the pipefor antibuoyancy purposes. The weight coating may take one of severalforms, including mastic type coating and high-density concrete coating.

Specifications normally call for a minimum quantity of coating materialto assure adequate weight for antibuoyancy purposes. Coatingapplicators, on the other hand, desire not to put on any significantexcess coating material since, to do so, would increase the cost of thecoating operation. Accordingly, it is the practice to continuallymonitor the amount of coating material applied to a pipe to be sure thatthe minimum quantity necessary for the minimum weight is present, butalso to be sure that large excesses resulting in wasted material are notapplied. The prior art techniques for monitoring the amount of coatingmaterial applied have taken two basic approaches. One of these is toweigh, periodically, a coated pipe joint to determine if the amount ofcoating material is correct. The disadvantage of this technique is thatdeficiencies or excesses in the coating processes only come to lightafter several joints of pipe have been coated.

The second basic approach is to periodically position a tape measurearound the pipe during the coating process to determine the diameterand, accordingly, whether or not the proper weight is being applied. Thedisadvantage of this technique is that the accuracy is never as high asdesired and the ability to take a measurement while coating is beingapplied varies greatly with the skill of the particular workmaninvolved. Furthermore, there is always some danger present for theworkman when approaching the pipe that is rotating at a high rate ofspeed. Even under the best of circumstances, such a measuring techniquecannot be practiced on a continuing basis as the coating is beingapplied to the pipe.

It is therefore an object of the present invention to provide a methodand apparatus to monitor the amount of coating material applied to apipe with much greater accuracy than has been possible with heretoforepracticed hand-held tape measuring devices.

Another primary object of the present invention is to provide a methodand apparatus for monitoring the amount of coating material applied to apipe whereby monitoring can be done continuously during the coatingoperation and any deficiencies or excesses of coating material correctedbefore no more than one joint of pipe is completely coated.

Another important object of the invention is to provide a method andapparatus for monitoring the amount of coating material applied to apipe whereby a continuous graphic record of the amount of materialapplied to each individual pipe section may be provided if desired.

It is also an important objective of this invention to provide a methodand apparatus for monitoring the amount of coating material applied to apipe whereby there can be automatic adjustment of the coating apparatusin response to the variations in the quantity of material which is beingapplied to the pipe.

A further object of the invention is to provide a method and apparatusfor monitoring the amount of coating material applied to a pipe whereinthe monitoring device may be rapidly moved into and out of its operativeposition, and which requires no manual labor once in operation.

It is also an aim of this invention to provide a method and apparatusfor monitoring the amount of coating material applied to a pipe whichcan accommodate simultaneous rotational and longitudinal movement of thepipe during the coating process and also the whipping action sometimesexperienced without resulting in false readings as to the amount ofcoating material being applied.

As a corollary to the above aim, it is an objective of the invention toprovide a method and apparatus for monitoring the amount of coatingmaterial applied to a pipe which is self-balancing and self-damping.

Another one of the objects of this invention is to provide a method andapparatus for monitoring the amount of coating material applied to apipe whereby different diameters of pipe may be accommodated using thesame basic method and apparatus.

Still another important object is to provide a method and apparatus formonitoring the amount of coating material applied to a pipe which cancontinuously operate during the coating process and which does notdamage the coating while in operation.

Other objects of the invention will be made clear or become apparentfrom the following description and claims when read in light of theaccompanying drawings wherein:

FIG. 1 is a front elevational view of the apparatus of the presentinvention shown in operable relationship to a coated section of pipe;

FIG. 2 is a greatly enlarged fragmentary sectional view showing amodified form of the invention whereby the measuring arm is coupled witha potentiometer;

FIG. 3 is another enlarged elevational view looking in the direction of3--3 of FIG. 1 and with portions broken away and shown in cross sectionfor purposes of illustration;

FIG. 4 is an enlarged cross sectional view taken along 4--4 of FIG. 1;

FIG. 5 is an end elevational view looking in the direction of 5--5 ofFIG. 4;

FIG. 6 is a fragmentary top plan view, on an enlarged scale, looking inthe direction of 6--6 of FIG. 1;

FIG. 7 is a schematic illustration of the manner in which the apparatusof the invention responds to whipping action of the pipe;

FIG. 8 is a diagram of an amplifier circuit used to amplify anelectrical signal generated by the monitoring device as the thickness ofthe coated pipe is monitored; and

FIG. 9 is a diagram of the electrical circuit which converts themeasurement obtained using the device of the present invention to adigital readout.

Referring initially to FIG. 1, the coating monitoring device of thepresent invention is designated generally by the numeral 10. The device10 is disposed in side-by-side relationship to a joint of pipe 12 towhich has been applied a relatively thick layer of concrete coatingmaterial 14. The device 10 is mounted upon two parallel angle ironsupports 16 each of which is provided with a plurality of alignedopenings 18 extending along its length. Mounted on the supports 16 is alongitudinally extending plate 20 which presents a monorail support fora movable support plate 22. Plate 22 in turn pivotally mounts agraduated vertical boom 24 having parallel, horizontally disposed firstand second sensing arms 26 and 28, respectively.

Referring in greater detail to the construction of movable support plate22 and the structure associated with it, these details of constructionare best illustrated in FIGS. 4 and 5. Support plate 22 is provided withfour flanged rollers 30 disposed in spaced apart relationship andengageable with the edges of rigid mounting plate 20. An electric motor32 is mounted on plate 22 and is the prime mover for a rubber drivewheel 34 to which the motor is coupled through suitable reductiongearing designated by the numeral 36. Manifestly, drive wheel 34 is infrictional engagement with plate 20. Two upstanding brackets 38 whichare rigid with plate 22 provide mounts for nut and bolt assemblies 41that serve as adjustable stops against movement of the boom 24 as willbe explained in greater detail hereinafter.

With particular reference to FIG. 5, it is seen that the triangularshaped nose of plate 22 supports a pivot pin 40 which is secured by anut 42 and which, in turn, mounts a winged U-shaped bracket 44. Nut andbolt assemblies 46 disposed on opposite sides of pivot pin 40 passthrough the wings of bracket 44 to secure boom 24 in rigid relationshipto the bracket. It can be seen in viewing FIG. 1 that the wings ofbracket 44 are provided with a plurality of openings 48 to accommodateadjustable positioning of the boom relative to pivot point 40 forpurposes to be more fully explained hereinafter.

Boom 24 is provided with graduations 50 along its length to permit firstand second arms 26 and 28 to be preset at the approximate outsidediameter of the coated pipe 12 and 14. Boom 24 is disposed in agenerally vertical plane and is of a length slightly greater than themaximum diameter of coated pipe which is to be monitored. First sensingarm 26 is mounted toward the upper end of boom 24 by means of a sleeve52 and adjustable tensioning screws 54 which pass through the sleeve tocontact the boom (see FIG. 2). A hinge coupling 56 joins sensing arm 26with the sleeve while still permitting pivotal movement of the arm. Tothis end, a pair of guide plates 58 (one of which is visible in FIG. 1)extend from arm 26 on opposite sides of sleeve 52 to guide the pivotalmovement of the arm.

Sensing arm 26 extends outwardly in generally perpendicular relationshipto boom 24, thereby occupying a generally horizontal plane. The sensingarm 26 is of a length somewhat greater than the radius of pipe 12 sothat the end of the arm may be positioned at approximately the locationof a vertical bisector passing through the pipe. Sensing arm 26 isprovided with a plurality of openings 60 for securing weights to thearm, if needed, for balancing purposes as will be explained in greaterdetail hereinafter. Arm 26 terminates in a yoke assembly 62 which mountsa roller 64 (see FIG. 6) that is in contact with the pipe coating 14.

Referring to FIGS. 2 and 3, at the end of arm 26 which is adjacent tosleeve 52 an ear 66 projects outwardly in transverse relationship to thearm to mount a coupler arm 68. One end 70 of arm 68 passes through ear66 and is threaded to permit adjustable positioning of the arm relativeto ear 66 via nuts 72. The other end of arm 68 is bent into an L and isreceived by a pivotal linkage 74. An L-bracket 76 which is rigid withsleeve 52 mounts a bushing 78 which in turn receives a pivotal shaft 80.One end of shaft 80 is rigid with pivotal linkage 74 and the other endof the shaft has rigidly mounted on it a pointer 82. Also mounted onbracket 76 between the long leg of the L and pointer 82 is a gaugedisplay panel 83 calibrated in accordance with anticipated variations inthe thickness of coating 14.

Second sensing arm 28 is mounted on boom 24 by a sleeve 84 and atensioning screw 86. There is no pivotal coupling between arm 28 andsleeve 84, rather the arm is completely rigid with the sleeve. Again, aswith the arm 26, openings 88 are provided along the length of the arm topermit mounting of weights for balancing purposes. Like arm 26, arm 28terminates in a yoke assembly 62 which mounts a roller 64.

In operation, plate 20 is first adjusted to a correct vertical height byproperly positioning it along angle iron supports 16. Manifestly,different pipe diameters will require plate 20 to be placed in differentlocations to accommodate different "heights" of the pipe. Next, motor 32is energized to drive wheel 34 and move the support plate 22 along plate20 until arms 26 and 28 are positioned in contact with the outer surfaceof coating 14. To this end, it will be appreciated that arms 26 and 28are positioned on boom 24 at diametrically opposed locations so that thedistance between the arms is approximately equal to the predetermineddesired outside diameter of the coated pipe necessary to provide theproper amount of coating material.

The pipe 12 will normally be rotated at a high rate of speed about itsaxis and simultaneously moved longitudinally as coating 14 is applied.The device 10 will not in any way interfere with the coating operationand is designed to be used simultaneously with application of thecoating material. Thus, rollers 64 ride along the applied coatingmaterial and as variations in the outside diameter of the coating occurarm 26 will ride up and down moving relative to stationary arm 28.Movement of the arm 26 will in turn move pointer 82 to indicate to atechnician the extent of deviations in the coating thickness.

A phenomenon that is invariable experienced during a pipe coatingoperation is a certain amount of "whipping action" of the pipe. This isattributable to the fact that a relatively long length of pipe (40 feetor more) is supported only at its outermost ends while being rotated ata relatively fast speed. Inherently, a certain amount of "flexing" ofthe pipe occurs and this may be enhanced if the pipe is not perfectlystraight along its longitudinal axis. The whipping action of the pipewhich occurs as a result of the foregoing has been illustrated in anexaggerated manner in the schematic showing of FIG. 7. An importantfeature of the device 10 is that it is designed to accommodate thewhipping action illustrated in FIG. 7 without giving false readings ofthe coating thickness. To this end, the location of pivot point 40 iscarefully selected between a vertical plane passing through the outerends of arms 26 and 28 and a vertical plane passing through the combinedcenter of gravity of the first and second arms (including all structureassociated with same) plus the vertical boom 24. Thus, in FIG. 7, pivotpoint 40 is located to the right of the combined center of gravity ofboom 24 plus arms 26 and 28.

Any movement of pipe 12 in a downwardly direction will result indownward pivoting of the boom and arm assembly about pivot point 40 as aresult of the weight of the pipe pushing against the arm 28. Thisdownward movement will not affect movement of the upper sensing arm 26since it is still free to ride along the coating and detect variationsin diameter. Distortions in the readings obtained through movement ofarm 26 could occur, however, when the pipe 12 moves back upwardly to itsnormal position but for the careful selection of the location of pivotpoint 40 as above described. As a result of this location which, in FIG.7, is to the right of the center of gravity, there will be torsionalforces in the direction of arrows A which will lift the boom and armassembly upwardly as the pipe moves upwardly. The same principle is usedto avoid spurious readings as a result of the flexing of the pipeupwardly as a result of the whipping action. Thus, when the pipe movesupwardly from its normal position, the same torsional forces whichlifted the assembly to its normal position will continue to act on theassembly to allow it to pivot about point 40 as the pipe moves upwardly.When the pipe moves back down to its normal position, the force of thepipe acting against arm 28 will exert a force in the direction of arrowsB to return the assembly to its normal position. From the foregoing, itis seen that the location of pivot point 40 is selected to one side ofthe center of gravity of the boom and arm assembly so that there willalways be a torque force acting on the assembly in the directions ofarrows A. This force is countered by the force of pipe 12 pushingdownwardly on lower arm 28. This downward force of the pipe is used tohold the assembly in a normal position when no whipping action occursand to return the assembly to normal position when an upward deflectionoccurs. On the other hand, the rotational forces acting about pivotpoint 40 act to return the assembly to its normal position whendeflected downwardly as a result of whipping action and also to raisethe assembly in unison with the pipe when the pipe deflects upwardly asa result of a whipping action. It is to be noted that the extent ofpivotal movement of boom 24 is always limited by adjustable stops 41.

Returning now to FIG. 2 of the drawings, an alternative embodiment ofthe invention is therein illustrated. A potentiometer is designated bythe numeral 90 and is mounted on sleeve 52. A slider arm extension 92projects from the potentiometer and is coupled with arm 68. Manifestly,movement of arm 68 in response to movement of sensing arm 26 istranslated to the potentiometer which produces an electrical signal thatis indicative of the amount of coating material applied to the pipe. Tothis end, it is to be noted that nuts 72 permit fine adjustment to the 0position of slider arm 92.

Referring now to FIG. 8, the above mentioned potentiometer is generallyindicated within broken line 100. The slider arm of this potentiometeris indicated by numeral 102 and is supplied with a regulated D.C.voltage potential at input 104. The two potentiometer output lines 106and 108 are fed into differential operational amplifier 110. Variableresistor 112 is provided to serve as a fine zero adjustment. Operationalamplifier 110 as connected in FIG. 8 acts as a precision voltageinverter and provides mulitplication of the input voltage by a constant.Through the proper selection of resistors 114, 116, and 118 a gain ofapproximately 100 (which defines a stable operating condition) can beobtained from operational amplifier 110. A second differentialoperational amplifier 120 is also provided in order to assure thestability of the first amplifier under excessive loading conditions.This amplifier acts as a non-inverting amplifier and by the properchoice of resistors 122, 124, and 126 also provides a gain of 100without any resulting change in output polarity. The output of thisamplifier is sufficient to drive a pen recorder (not shown) and can beencoded to provide a digital display of pipe diameter.

In operation, the relative movement of sensing arm 26 is imparted to theslider arm of the potentiometer thereby producing an electrical signalrepresentative of the amount of coating material that has been appliedto the pipe. The produced electrical signal is then amplified inoperational amplifier 110. Since the resulting output of operationalamplifier 110 represents the difference between the two inputs frompotentiometer 100, the output is a linear function of the change of theoutside diameter of the coated pipe around a given zero position. Theresulting output of operational amplifier 110 is further amplified indifferential operational amplifier 120. The output of this amplifier canthen be sent to a voltage meter to give a voltage reading representativeof the coating thickness about a given zero point, a pen recorder toprovide a permanent record of variations in the coating thickness abouta given zero position, or the encoder circuit of FIG. 9 to produce adigital display of the pipe diameter.

Referring now to FIG. 9, the amplified D.C. voltage signal from theamplifier circuit of FIG. 8 is fed into the digital encoder circuit atinput terminal 130. Initiation of the encoding operation is accomplishedby closing reset switch 133. Closure of this switch serves to resetoutput register 138, memory register 136, sample counter 140, and SRBistable 132 and to initiate the operation sequence of the encodercircuit. The respective timing signals needed to clock the appropriatelogic circuitry of the encoder circuit are derived by combining theoutputs of SR Bistable Circuit 132 with the output of clock generator134 in suitable logic circuitry.

The incoming D.C. voltage signal from the amplifier circuit is initiallyconverted into a BCD signal in A/D converter circuit 142. The A/Dconverter has an input range of -5 to +5 volts in order to encompass awide range of possible coating thicknesses about the zero position.Since the converter uses -5 volts as its reference voltage, an inputsignal of zero volts (representative of no deviation from the zeroposition) is 5 volts above the reference voltage and will be convertedinto a BCD signal of 0101. Therefore, the output of this circuitrepresents an adjusted coating thickness figure.

The digital signal from the A/D converter is then sent to adder circuit144 where it is summed with the total of the previous adjusted thicknesssamples stored in memory register 136. The resultant sum is then storedin the memory register and sample counter 140 is incremented by onecount. The above described conversion, addition, and storage sequence iscontinued until a stop signal is received from stop switch 146. Itshould also be noted that the D.C. input voltage from the amplifiercircuit is inhibited during the addition and storage operations so thatthe coating thickness is measured at regular intervals along the pipe.

Upon the receipt of a stop signal, the resultant sum of the adjustedthickness samples stored in the memory register is divided, in dividercircuit 148, by the number of count states stored in the sample counterto give the adjusted average coating thickness over the samplinginterval. Thereafter, the adjusted average coating thickness figure issummed in adder circuit 160 with the outside diameter of the pipepreviously stored in output register 138. The outside pipe diameterfigure is punched into the encoder circuit by means of a calculator typekeyboard 150. Subtractor circuit 152 then subtracts the output from zerogenerator 154 (in this case 0101) from the output total of adder circuit160 to give the true diameter of the coated pipe. Depression of readbutton 162 reads the output of the subtractor circuit into outputregister 138 and decoder circuit 156 continually decodes the contents ofthe output register to give 4 figure display of the diameter of thecoated pipe at 158.

The output signal from the above described amplifier circuit of FIG. 8can also be fed into two center zero type pen recorders (not shown) inorder to provide a method for manually checking the accuracy of thedecoder circuitry. The first recorder can be set up to give a constantchart of the outside diameter variations about said zero position andthe second recorder can be set up to make a permanent record of theaverage reading accepted by the computation circuits. The informationrecorded by these two pen type recorders can then be used to check theaccuracy of the encoder circuit by ordinary mathematics.

It will also be apparent to those skilled in the art that the presentinvention contemplates a method for monitoring the amount of coatingmaterial applied to a cylindrical pipe utilizing a device as hereindescribed. Manifestly, the method encompasses positioning the first andsecond arms of the device on the pipe in diametrically opposedrelationship and allowing one arm to move in response to varyingdiameters of the coated pipe. The extent of movement of the one arm isobserved to determine the amount of coating material being applied. Themovement may be translated into an indication of the coating thicknessand simply manually recorded or may be continuously recorded byautomatic recording equipment. A further step of the inventioncontemplates that the step of observing the movement of the movable armwill take the form of translating a signal from the arm to the apparatuswhich is applying the coating material to vary the amount of materialused in response to the observed measurement.

As previously mentioned, openings 60 and 88 in arms 26 and 28,respectively, may be utilized to secure weights for counterbalancing thetorsional forces which tend to move the assembly in a counterclockwisedirection when viewing FIG. 1. Particularly where shorter arms aresubstituted for arms 26 and 28, it may be necessary to affix weights forcounterbalancing purposes. Also in this regard, boom 24 may be securedthrough any one of the aligned sets of holes 48 in bracket 44. Byshifting the boom 24 to either the left or the right, the center ofgravity of the unitary assembly comprising the boom plus the arms isaccordingly shifted.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:
 1. A device for monitoring theamount of coating material applied to the outside of a rotatingcylindrical pipe which is unaffected by any whipping action of the pipe,said device comprising:rigid support means; elongated mounting meanscoupled with said support means and disposed in a generally verticalplane; first and second sensing arms carried by said mounting means forcontacting the surface of the coated pipe, one of said arms beingpivotally coupled with said mounting means at a point above the secondarm, the outer end of said one arm being pivotally movable up and downin accordance with variations in the thickness of the pipe coating; andmeans for pivotally coupling said mounting means with said supportmeans, said means for pivotally coupling said mounting means with saidsupport means being disposed between a vertical plane passing throughthe outer ends of said sensing arms and a vertical plane passing throughthe combined center of gravity of said sensing arms plus said mountingmeans.
 2. A device as set forth in claim 1, wherein said means forpivotally coupling said mounting means with said support means includesadjustable positioning means for varying the relative positions of saidcenter of gravity and said pivotal coupling.
 3. A device as set forth inclaim 1, wherein is included means for displaying said variations in thethickness of the pipe coating.
 4. A device as set forth in claim 3wherein said means for displaying the variations in the thickness of thepipe coating comprises a gauge, and indicator means coupled with saidone arm for movement in response to movement of the arm, said indicatormeans also being associated with said gauge for displaying a measurementof said variations in thickness.
 5. A device as set forth in claim 4,wherein said means for displaying the variations in the thickness of thepipe coating comprises a potentiometer having a slider arm coupled withsaid one movable arm, and means coupled with said potentiometer fordisplaying an output in response to the voltage signal produced by thepotentiometer.
 6. A device as set forth in claim 5, wherein saiddisplaying means comprises:means for encoding said voltage signal into adigital signal, and means coupled with said encoding means fordisplaying an output response to said encoded digital signal.
 7. Amethod for monitoring the amount of coating material applied to theoutside of a rotating cylindrical pipe, which method is unaffected byany whipping action of the pipe, said method comprising:providing firstand second sensing arms for contacting the surface of the coated pipe,said arms being coupled together in a unitary assembly mounted formovement about a pivot axis; locating said pivot axis at a positionbetween a vertical plane passing through the center of gravity of saidassembly and a vertical plane passing through the outermost ends of saidarms thereby providing a torque force for countering pivotal movement ofsaid assembly about said axis; positioning said arms to contact thecoated pipe in generally parallel horizontal planes at diametricallyopposed locations; the pipe contacting portion of the uppermost armbeing movable up and down with respect to the lower arm in response tovariations in the thickness of the pipe coating; and sensing the extentof movement of the uppermost arm with respect to the remainder of theassembly.
 8. A method as set forth in claim 7, wherein is included thestep of translating the movement of said uppermost arm into an indicatorof the thickness of the coating material.